linux-kernel - Re: [RFC PATCH v6 24/32] perf record: Compile scriptlets if pass '.c' to --event

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Date:	Wed, 10 Jun 2015 08:06:17 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Alexei Starovoitov <ast@...mgrid.com>, <acme@...nel.org>,
	<brendan.d.gregg@...il.com>, <daniel@...earbox.net>,
	<namhyung@...nel.org>, <masami.hiramatsu.pt@...achi.com>,
	<paulus@...ba.org>, <a.p.zijlstra@...llo.nl>, <mingo@...hat.com>,
	<jolsa@...nel.org>, <dsahern@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<hekuang@...wei.com>, <xiakaixu@...wei.com>, <pi3orama@....com>
Subject: Re: [RFC PATCH v6 24/32] perf record: Compile scriptlets if pass
 '.c' to --event



On 2015/6/10 5:48, Alexei Starovoitov wrote:
> On 6/8/15 10:50 PM, Wang Nan wrote:
>> +struct bpf_param bpf_param = {
>> +    .clang_path = "clang",
>> +    .llc_path = "llc",
>> +    .clang_opt = "",
>> +    .llc_opt = "",
>> +};
>
> the defaults are ok-ish, but llc is never in PATH.
> So most likely it won't work out of the box.
> I think the cleanest option is too wait a little bit
> until we finish clang integration.
> (hopefully few more days)
>
> we've quite been busy on llvm side
> and I'm excited to announce that BPF backend finally
> graduated from experimental.
> So now anyone can just pull the latest llvm and
> bpf will be present by default.
> No more cmake -DLLVM_EXPERIMENTAL...
>
> Once clang integration is complete. One can pull
> upsteam llvm and clang and just use 'clang -O2 -c -march=bpf file.c'
>

Good news, so llc part should be removed.

Next version I'd like to use following config options:

[llvm]
     clang-bpf-cmd-template = "$CLANG_EXEC $CLANG_OPTIONS -c 
$CLANG_SOURCE -emit-llvm -O2 -o - | /path/to/llc -march=bpf 
-filetype=obj -o -"
     clang-path = "/path/to/clang"
     clang-opt = ""

And the default template should be:

$CLANG_EXEC $CLANG_OPTIONS -c "$CLANG_SOURCE" -emit-llvm -O2 -o -

Then with environment variable tricks we make it work with popen.

By this way we can get rid of llc in perf side, and make it work even 
before clang
integration is complete.

Thank you.

>> +    err = WEXITSTATUS(pclose(file));
>> +    if (err || read_sz <= 0) {
>> +        err = -EINVAL;
>> +        pr_err("Error:\tsomething went wrong when compiling %s\n",
>> +               filename);
>> +        pr_err("Hint:\tTry manually run following command and 
>> check:\n");
>> +        pr_err("  # " CMD_FMT "\n\n",
>> +               clang_path, bpf_param.clang_opt, filename,
>> +               llc_path, bpf_param.llc_opt, "/dev/null");
>
> not terribly informative hint.
> I think would be good to point to some readme or at least mention
> that only the latest clang/llvm support bpf.
> Either svn/git trunk or upcoming 3.7
> May be a link to llvm.org?
>


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